You don't see all parts of the world equally well. An obvious example is the way your peripheral vision is much fuzzier than your central vision. Now Richard Abrams and colleagues have provided a far more curious example - apparently the mere presence of our hands alters the way we process visual information in their vicinity.
On hundreds of trials, 52 participants sought to identify as fast as possible whether it was an 'H' or an 'S' that was hidden among a crowd of 'E's and 'U's displayed on a computer monitor.
Bizarrely, participants were significantly slower at the task when their hands were placed either side of the computer screen (nearer the stimuli), as opposed to being located on their laps.
Importantly, the hands' proximity to the stimuli still exerted this effect even when they were hidden behind cardboard, and also when participants responded using foot pedals. In other words, it was the hands' mere location in space that affected visual processing - it wasn't the sight of them, or to do with their being used to respond.
A second experiment showed that the presence of the hands near the computer screen made participants take longer to disengage their attention from a target that appeared abruptly on the screen. A final experiment, showed that the presence of the hands led to a prolonged 'attentional' blink - this is our tendency to miss the second of two targets appearing in a stream, if the second appears too soon after the first.
Across all three experiments, the message seems to be that the presence of the hands makes it harder for us to disengage our visual attention from a target. Why should this be? "One possibility," the researchers said, "stems from the fact that objects that are near the hands are likely candidates for physical manipulation [such as a tool or food]...In those circumstances, extended analyses of objects near the hand may facilitate the production of accurate movements."
ABRAMS, R., DAVOLI, C., DU, F., KNAPPIII, W., PAULL, D. (2008). Altered vision near the hands. Cognition, 107(3), 1035-1047. DOI: 10.1016/j.cognition.2007.09.006